The proposed research will investigate control of behavior by temporally-patterned events, with an emphasis on the discriminability of time-based schedules of reinforcement, including both fixed- and variable-interval schedules. The outcome of this work will be the development of a scale relating subjective reinforcement density to objective reinforcement density. The individual stimulus dimensions which contribute to control of behavior by patterns of events will be analyzed. In addition, the rule which best describes the manner in which sequences of time intervals combine to control behavior will be determined. This will include consideration of temporal control per se, as this is probably crucial to analysis of control by rate. Finally, the results obtained above will be applied to behavior in a choice situation, in an attempt to disentangle the motivational from the discriminative properties of schedules. It is hoped that a clearer understanding of the stimulus properties of schedules will produce a better understanding of behavior in choice situations.